This invention proposes a universal stereoscopic viewer that by means of modifying the current lens-slide distance used up to the present, affords any user a sharp, clear three-dimensional vision of a pair of images. Up to the present, a great deal of equipment has been made which makes it possible to obtain a three-dimensional vision using an appropriate pair of two-dimensional images especially the kind that use a pair of slides. All such equipment is constructed to obey the following relationships: EQU D=F and EQU A=B
where
D represents the distance between the slides and the lenses, PA1 F is the focal distance of the lenses through which the images must be viewed, PA1 A is the distance between the optic axes of these lenses and PA1 B is the distance between the centers of these images.
This stereoscopic equipment is non-universal for various reasons. First of all, the two lenses are always at a distance of 63-65 mm., a distance which is considered to be the average distance of the interpupillary distances of the users (children have an interpupillary distance of 55 mm., macrocephalous people: an interpupillary distance of 85 mm.) have in addition, since the images are also 63-65 mm. far from each other and at the same distance as the focal distance of the lenses, the combinations are virtually endless.
Now, according to some surveys done by the inventor of this device, whenever a person looks at an object, his or her eyes, depending on the distance between him or her and the object, automatically converge at a certain angle and the crystalline lens contracts in order to focus the object in question; these two movements of convergency and focusing are very much tied together and dependent upon each other. Also, it has been shown that when a person looks at a moving object at a distance greater than 10 meter, normally he or she tends to turn his or her head rather than move his or her eyes (the typical movement of spectators at a tennis match) whereas for smaller distances, the person tends to move his or her eyes rather than his or her head. We can deduce that at a certain distance, the eyes acquire a certain inertia or "laziness".
Considering the above observations, the user who looks into one of the stereoscopic devices that are on today's market, finds that he or she is looking at two images virtually at infinity that nevertheless, contain three dimensional details that are much closer (3-5 meter); thus the user must make a preliminary effort to disassociate the ocular convergency movement from the focusing movement.
Secondly, in order to look at the various details in the two images, he or she must make another effort to overcome the inertia or "laziness" of his or her own eyes in viewing different objects but which are all practically without end.
In addition, the users who have an interpupillary distance which is less then the considered average (63-65 mm.) are, indeed, required to diverge their eyes which is very difficult to do since it is absolutely unnatural.
These problems in perceiving a correct three dimensional vision frequently lead to a general and sudden fatigue of the user's entire visual apparatus and often cause trouble such as headaches, a feeling of nausea or dizziness.
According to recent statistics, because of these side effects, only 9% of the users are able to perceive a correct vision of the three-dimensional effect in these devices without experiencing the above-mentioned manifestations.
Furthermore, there is stereoscopic equipment with variable adjustment that, however, besides being more complicated and expensive, requires delicate calibrations depending on the interpupillary distance of the user.